Modem backplanes, also referred to as motherboards, serve as a communication medium for the exchange of electronic signals between a plurality of daughter cards. Circuitry on each daughter card generates communication signals, which are distributed to connectors mounted along an edge of the daughter card. Daughter card connectors mate with a corresponding set of backplane connectors typically arranged in equidistant rows on the backplane for providing interconnect and distribution of signals therebetween.
A chassis houses the backplane, daughter cards, and corresponding connectors. The chassis frame includes side panels and cross members, also referred to as extrusion rails. Card guides mounted on the extrusion rails run from the front to the rear of the chassis to guide the daughter cards into proper alignment with corresponding backplane connectors. Each daughter card position in the chassis is referred to as a card slot. The relative positioning of the card guides with respect to the mother board is critical, since the relative positioning determines how well the daughter card connectors align with the motherboard connectors during daughter card insertion. Consequently, motherboard alignment has traditionally required special tooling and procedures, and has been a tedious and time-consuming portion of chassis assembly.
In general, daughter cards to be inserted into a motherboard chassis assembly may accumulate a significant static charge during storage and handling. This static charge must be discharged prior to electrically coupling the daughter card to the system via the motherboard connector, so as to prevent ESD damage to the system. In addition, the front panel assembly of a daughter card may include a number of cable connectors electrically coupled to external cables. Such cables and cable connectors may also provide a source of significant static charge which must be discharged to prevent ESD damage to the system. A number of prior art methods exist for discharging daughter card ESD and for discharging front panel ESD. However, such prior art methods typically utilize separate, distinct mechanisms for discharging each source of static charge.
During operation, the electrical components on the daughter cards generate heat which must be extracted to prevent thermal damage. A popular means for inducing heat transfer is a cooling apparatus which forces a volume of cooled air through the chassis. The cooled air removes heat from the electrical components by means of thermal convection. The resulting warmed air is ventilated, or otherwise cooled and re-circulated.
As air flows past structural features on the chassis, for example the extrusion rails, the interference causes turbulence in the air flow. Turbulence results in regions of marginal air flow, which if proximal to the daughter cards, can cause xe2x80x9chot spotsxe2x80x9d to form on the daughter cards. To avoid this problem, card designers refrain from populating components in the xe2x80x9chot spotxe2x80x9d regions, and card surface area is therefore underutilized. This is a most undesirable approach because as electronics become increasingly sophisticated, daughter card surface area is at a premium.
U.S. Pat. No. 4,750,088, issued Jun. 7, 1988 and incorporated herein by reference, addresses this issue by providing a number of air deflectors having a wedge-shaped cross section. The deflectors are extruded members mounted across the top and bottom portions of the chassis, parallel to the extrusion rails, for directing cooling air into marginal areas of the daughter cards, proximal to the extrusion rails. However, this configuration complicates construction of the chassis by requiring additional hardware, which, in turn, lengthens the time and cost for production of the chassis assembly.
In a first aspect, the present invention relates to card guides, and more particularly to card guides which optimize the flow of forced cooling air, provide for self alignment to a host motherboard and provide for integrated ESD hazard mitigation. The present invention is directed to a card guide configured to maximize air flow across circuit boards mounted in a card cage in a manner which mitigates and/or eliminates regions of marginal air flow. As a result, circuitry can be populated on the daughter card in regions proximal to the extrusion rails, allowing for more efficient use of daughter card surface area.
The present invention achieves this result in a manner which overcomes the limitations of the prior art. Specifically, air deflectors are incorporated into the body of the improved card guides, and the improved card guides are mounted to the chassis in a manner similar to the manner in which standard card guides are mounted. Unlike the prior art technique described above, additional hardware is not needed to redirect air flow about the extrusion rails and construction of the chassis is simplified.
A card guide in accordance with the present invention is adapted for mounting to a circuit card chassis having extrusion rails or cross members. The card guide is further adapted for channeling a daughter card toward a motherboard assembly, so as to ensure proper registration of the daughter card connector with a motherboard connector. The card guide comprises an elongated body having a groove along its longitudinal axis for receiving the edge of a circuit card. The body is adapted for mounting to the extrusion rails. At least one air deflector is laterally coupled to the body, and extends in a direction substantially transverse to the longitudinal axis for redirecting incident air flow about the rail.
In a preferred embodiment, the air deflector is integral with the card guide. The air deflector is preferably arcuate in cross section to optimize the efficiency of air flow. Fabrication of the card guide may be accomplished via injection molding techniques, or by other techniques known in the art. Standard mounts are preferably included at opposite ends of the card guide body for mounting the card guide to the extrusion support rails. Additional air deflectors, integral with the mounts, may also be included. Mounting features of the mounts may include a latching mechanism which extends transversely from the body of the card guide, and fixedly engages a corresponding aperture in the support rail.
In a second aspect, the body of the card guide includes an ESD clip having a base, a wiper blade and a barrel receptacle, all three of which are electrically conductive and electrically coupled to one another. The base of the ESD clip includes a terminal for electrically coupling to the extrusion support rail. The wiper blade extends through the body into the groove along the longitudinal axis, so as to facilitate electrical coupling to a conductive edge of the daughter card. The barrel receptacle is disposed adjacent to and coaxial with a guide aperture in the card guide body. When a daughter card is inserted into the chassis and mates with the motherboard, the barrel receptacle receives and electrically couples to an electrically conductive guide pin fixedly attached to a front panel of the daughter card.
In a third aspect, the body of the card guide includes an alignment pin, fixedly attached to an end of said body proximal to the motherboard assembly. The alignment pin extends from the body in a direction substantially parallel to the longitudinal axis, and is operative to engage a corresponding aperture in said motherboard, so as to substantially align the card guide to the motherboard.